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any way i can make a mold of plastic with out breaking it? Answered

any way i can make a mold of plastic with out breaking it? the plastic is knex and i need to know how to make a mold for it and it must withstand the heat of metal update:pic of what i want molded

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GrathioBest Answer (author)2009-08-05

I agree with frollard, you have a very difficult project here. I have experience casting plastic and I wouldn't attempt something this complex. It would be a waste of materials. It looks at very least a 3 or 4 part mold if you want to cast is tall as one piece. (If not, it's several two piece molds.)

If you want to make it out of cast metal I would probably use some version of the lost wax technique. In this case I might try it with "lost plastic" where I cast the full plastic and then burn it out, though I'm not sure if it would burn off clearly enough to get a good mold. Also getting a proper cast of this shape without any voids would take a lot of luck.

However it looks like you'd don't need all of the detail in this piece. In that case I might take the Kinex, fill in the details I don't need with putty or clay and make a two part silicone mold. From the mold I'd make several copies in Jeweler's wax and use them to make lost wax casting (liked above).

Note that whatever way you do it will introduce small imperfections into the object which may not make it suitable for your purpose.

Good luck!

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Oblivitus (author)2009-09-12

Haha, this is my signature firing pin design.

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An Villain (author)2009-08-19

i would suggest using metal for strength, steel would be best, to cast use the cira perdue technique as suggested by ookseer.

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lemonie (author)2009-08-05

You could mould with silicone, create a wax pattern from that (very difficult to do without breaking it) and try a lost-wax casting (very difficult to do with such a thin piece) L

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frollard (author)2009-08-04

If I understand correctly, you want to make a mold of an assembled knex object? there are so many undercuts it would be near impossible. Molding silicone is probably the best bet, and it can then be used to mold lower temperature metals like lead and pewter.

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the new pic might help but im using alumin cans melted down

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that is really rediculously difficult :( is it possibly easier to fabricate them by cutting down larger material (milling) rather than forging/molding. Very small detailed parts like this (even if not detailed, small) are quite hard to cast, and often use a centrifugal forge to ensure theres enough pressure to get the metal into the mold.

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steveastrouk (author)2009-08-05

Why does it have to be this Knex object ? Could you simplify its shape, and make a wooden or wax pattern ? Casting wax could be done "lost wax" process ?

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